Want to scrape the muck out of your company's job applicant pool? Just head for your favorite social networking site.

By now, anyone with a functioning frontal lobe should know that their online behavior -- or misbehavior -- is always just a Google search away. That's why the latest annual CareerBuilder survey offers some sobering results.

As social networking grows increasingly pervasive, more employers are utilizing these sites to screen potential employees. Forty-five percent of employers reported in a recent CareerBuilder survey that they use social networking sites to research job candidates, a big jump from 22 percent last year. Another 11 percent plan to start using social networking sites for screening. More than 2,600 hiring managers participated in the survey, which was completed in June 2009.

Of those who conduct online searches/background checks of job candidates, 29 percent use Facebook, 26 percent use LinkedIn and 21 percent use MySpace. One-in-ten (11 percent) search blogs while 7 percent follow candidates on Twitter.

Guess what? More than a third of the employers surveyed said they have rejected a candidate based upon information they post online. The most frequently cited examples: "Provocative or inappropriate photographs or information" (53 percent); "content about [the candidate] drinking or using drugs" (44 percent); and candidates who "bad-mouthed their previous employer, co-workers or clients" (35 percent).

Other contenders for the World's Dumbest Job Applicant trophy include bigots, bad liars, and folks who don't understand the meaning of the term "confidentiality agreement."

There is a happy ending of sorts to this story. One employer in five said they found online content that actually caused them to hire a candidate. Job seekers who treat their online identities as extensions of their resumes are thus very likely to benefit from their diligence.

Something else came as a surprise here: the fact that so many employers still don't perform these types of de facto background checks. A fact-finding trip through the top social networking sites is fast, easy, free -- and, it seems, very likely to turn up relevant information.

Just don't forget that online research is a tool, not a crutch. Slander is practically a competitive sport on some sites, and mistaken identity is potentially a big problem. Context matters; if your company treats an online background check like a glorified keyword search, it is just as likely to reject candidates based upon unfair or inaccurate information.

Besides, if the CareerBuilder survey is any guide, there are already more than enough truly incompetent job-seekers wandering the world's social networking sites to keep your HR staff busy.